Showing papers in "Medical & Biological Engineering & Computing in 1974"

Development of active anthropomorphic exoskeletons

Abstract: The basic postulates of this new approach to the study of anthropomorphic systems dynamics are given in the paper. In comparison with other attempts, this approach enables the maximal reduction of dimensionality, being based on prescribing synergy, to one part of the system. As an illustration of the method, an example is given of a complete synergy synthesis for the adopted configuration of the anthropomorphic systems.

Mechanical properties of human cancellous bone in the femoral head.

Abstract: The ultimate compressive strength of human cancellous bone derived from femoral heads was found to range between 21 and 1963 Ibf/in2 (145-13535 kN/m2). A correlation coefficient of 0·70 was found for the relationship between compressive strength and apparent density of cancellous bone; however, no statistically significant correlation was found between compressive strength and location of the cancellous bone within a femoral head. The stress relaxation of cancellous bone, measured at widely differing initial stresses, demonstrates the viscoelastic nature of cancellous bone, and consequently the tendency to flow or creep under time-dependent stresses.

Theory and design of capacitor electrodes for chronic stimulation.

Abstract: Conventional metal electrodes generate electrochemical byproducts during stimulation of nerve or muscle. These byproducts may cause tissue damage, especially with the long-term stimulation necessary with neural prosthetic devices. To prevent the possibility of such damage, completely insulated electrodes have been devised which deliver current pulses by capacitive charging of the electrode surface, not involving electrochemical reactions. Anodised discs of porous tantalum, 1·0 mm in diameter and 0·25 mm thick, can deliver 0·5 ms, 5 mA pulses. Such electrodes are available as components of commercial capacitors and are easily adapted for biological use. The design may be optimised by mathematical analysis of an equivalent electrical circuit.In vitro tests demonstrate a clear advantage of these electrodes over capacitively coupled platinum-iridium electrodes in preventing oxidation-reduction reactions. The electrodes are stable on chronic implantation and should provide a safer interface between neural prosthetic devices and human tissue.

The analysis and simulation of the human thermoregulatory control system.

Abstract: The paper describes a study into one aspect of the thermoregulatory control system in man. An analysis of this control system led to the hypothesis that thermoregulation in humans is achieved by two basic control systems that act as first and second lines of defence and that influence each other. Available physiological information has been utilised in a digital computer simulation of the vasomotor activity associated with the first stage of human thermal control. In exploring features of the model it has been shown that the incorporation of on-off control allows two key aspects of the control system associated with thermal vasomotor activity to be duplicated: (a) the spontaneous fluctuations in digit blood flows; (b) the ability of a thermally induced disturbance to entrain these spontaneous fluctuations. It has also been possible to illustrate driving frequency dependence of the entrainment phenomenon both in the physical system, by physiological experimentation, and in the computer model.

A mathematical model of the slow-wave electrical activity of the human small intestine.

Abstract: Based on available data of the slow-wave electrical activity in the small intestine of humans and dogs, a mathematical model has been developed. The model comprises an interconnected chain of 100 Van der Pol relaxation oscillators with the method of coupling and its magnitude chosen so that known phenomena in the small intestine are reproduced by the mathematical model. Results from digital simulations on an ICL 1907 computer are presented which show how the model matches the data from the small intestine. Further phenomena such as a travelling area of reduced frequency along the oscillator chain have also been found, and it is shown that this effect is related to the phase relationships along the chain.

X ray spectrophotometry for bone-mineral determinations.

Abstract: This X ray spectrophotometer is designed for bone-mineral and soft-tissue determinations on adult humans The equipment comprises an X ray tube with a special high-voltage generator and a filtering unit to produce two narrow energy bands, a system composed of two servocontrolled measuring wedges with attenuation properties corresponding to bone-mineral and soft tissues, respectively, a scintillator photomultiplier detector and a feedback loop coupled to the servocontrolled wedges The wedges are automatically kept in such a position that the X ray fluxes are constant at the scintillator When the object is placed in the beam, the wedges are automatically withdrawn, the displacements constituting a quantitative measure of the analysed substances in the transversed volume of the object The system has a high degree of stability and precision Determinations take from 2 to 20 s, depending on the level of precision required

A model for myoelectric signal generation.

Abstract: A myoelectric signal, under isometric contraction of the muscle, is modelled as the output of a linear time-invariant system whose input is a stationary Poisson pulse train. The mean frequency γ of the Poisson pulse train and the transfer function of the linear system are evaluated using the spectral properties of the signal. An estimate of the number of active motor unitsN contributing to the myoelectric signal is obtained under the assumption that the individual motor-unit trains are statistically independent. The variation of γ andN with respect to load levels and electrode positions is examined experimentally.

An equivalent diagram for the interface impedance of metal needle electrodes.

Abstract: Based on a consideration of the physicochemical processes in the interface between a metal electrode and an electrolyte, an equivalent circuit is derived for the small-signal impedance of metal bioelectrodes of the needle type. The equivalent circuit consists of four blocks: the charge-transfer section, which is essentially resistive; the double-layer capacitance, which operates in parallel to the first block; in series with the two is the diffusion-layer impedance, which decreases essentially with √ω and has a constant phase angle of 45°. It can conveniently be modelled by the input impedance of an infinitely longRC electrical transmission line with distributed parameters. And finally, in series with the latter, there is the bulk resistance of the electrolyte.

Computation of the impedance characteristic of metal electrodes for biological investigations.

Abstract: In a previous study, basic electrochemistry was used to derive analytical expressions for the equivalent network components of the ac impedance of biological needle electrodes In the present paper, numerical parameter values are determined and inserted into these expressions Matching of computer-calculated characteristics with experimental results has been used to determine certain constants, which are difficult to determine in a more direct way The electrode impedance at very low frequencies turns out to be almost purely resistive in character and mainly determined by the exchange current density of the metal-electrolyte system In the intermediate-frequency range the diffusion impedance together with the double-layer capacitance are the decisive factors The magnitude of the impedance diminishes here with fn, where −1

Fracture energy of bone in a shear mode

Abstract: The role of the osteon as the basic strengthening unit of compact bone is discussed. Using previous work on the shear strength of bone, an analysis is given enabling a computation to be made of the mode-II (debonding) fracture energy. The evidence suggests that bone, like many reinforced composites, derives its excellent fracture characteristics from the existence of a week osteon-matrix interface.

Tensile testing of connective tissues.

Abstract: This paper is concerned with the determination of the mechanical properties of connective tissues by subjecting them to uniaxial tensile loading. The emphasis is upon techniques which can be applied to a wide variety of tissues, and particular attention is paid to such problems as specimen form, cross-sectional-area measurement, gripping the specimen, providing a suitable test environment and measuring specimen extension.

Digital filtering of the e.c.g.—a comparison of low-pass digital filters on a small computer

Abstract: Algorithms for moving average, recursive and “Fourier transform” low-pass linear digital filters are described, with reference being made to the methods of design. The characteristics, including frequency, phase and impulse responses, of four specific filters are discussed in detail. In addition, some of the practical problems of programming these filters are considered. Factors such as execution times are evaluated in concluding which designs are most appropriate for filtering electrocardiograms.

A prototype flexible microelectrode array for implant-prosthesis applications

Abstract: This paper describes techniques for the fabrication of flexible microelectrodes for recording and stimulation within the human body. The intention of the effort was to develop a prototype microelectrode array for selective electrical stimulation of the cochlear nerve in cases of profound sensory deafness. The prototype array is formed on both sides of a thin-film plastic insulating substrate† and consists of platinum conductor-elements, 0·3 μm thick and 12·7 μm wide, terminating at electrode surfaces, 250 μm wide. Metallisation of the substrate is accomplished by sputtering, and the electrode patterns are defined by photolithographic-etching techniques. Insulation of the array is achieved by dip coating in Silastic. Short term (nonstimulated) animal-tolerance studies indicate that the electrodes are biologically inert. Long-term implant studies are currently in progress, and experiments are planned to determine tissue-reaction and electrolytic-dissolution effects due to prolonged electrical stimulation. Microelectrodes using the fabrication techniques described can be applied, in practically any geometry desired, to the development of functional sensory and motor prostheses. Cet article decrit des techniques de fabrication de microelectrodes flexibles servant a l'enregistrement et a la stimulation a l'interieur du corps humain. Ces travaux avaient pour but de developper le prototype d'un systeme de microelectrode pour la stimulation electrique selective du nerf cochleaire dans les cas de sourdesse sensorielle profonde. Le systeme prototype est forme de part et d'autre d'un film plastique fin d'une substance isolante (Mylar, Teflon ou Parylene) et consiste d'un element conducteur en platine de 0,3 μm d'epaisseur et de 12,7 μm de largeur, se terminant aux surfaces d'electrodes de 250 μm de largeur. La metallisation de la substance se fait par crepitement et es traces de l'electrode sont accomplis par des techniques de gravure photolithographique. L'islolement du systeme se fait par plongee dans un bain de Silastique. Des etudes de tolerance a court terme sur animaux (non stimules) ont indique que l'electrode est biologiquement inerte. Des etudes d'implantation a long terme sont en course, les experiences ont pour intention de determiner les reactions des tissus aux effets de dissolution electrolytique causes par une stimulation electrique prolongee. Les microelectrodes confectionnees d'apres les techniques decrites, peuvent etre appliquees selon pratiquement n'importe quelle geometrie desirees, au developpement de protheses motrices et sensorielles fonctionnelles.

Impedance measurements on metal needle electrodes.

Abstract: The paper brings the results of measurements of the impedance characteristics of metal needle electrodes made from a variety of metals. It is shown that the magnitude and frequency dependence of the impedance of highly polarisable electrode systems are, in general, similar. Of the metals examined, silver and mainly indium show a markedly different behaviour. Hope is expressed that further work could produce an indium-based electrode system which might, for certain applications, be superior to presently used electrodes.

Computer-terminal operating and communication aid for the severely handicapped.

Abstract: A communication aid that is suitable for use by the severely handicapped such as those suffering from high-level spinal injury has been developed. The system is based on the assembly of ASCII coded characters by means of a 2-level input employing a short cut. It has been used with a teletype computer terminal and a typewriter.

Leg load warning system for the orthopaedically handicapped.

Abstract: A system has been developed which measures the load applied to the heel of an ambulatory patient, compares that load with preset, adjustable (i) min imum required and (ii) maximum allowable loads as prescribed by a physician or physiotherapist, and reinforces the correct walking motion of the patient by turning off a low-frequency audible tone when the minimum load is exceeded, and turning on a high-frequency tone when the maximum load is exceeded. This system will be useful in allowing the physician and physiotherapist to control the walking performance of amputees and other lower-extremity patients during progressive weight-bearing training by helping the patients limit their weight bearing to a prescribed range.

Determination of the bone-crystallites distribution function by x ray diffraction.

Abstract: It is considered that meaningful interpretation of the physical properties of bone is possible only when the crystalline quality of bone is also known quantitatively. From the crystalline structure and the X-ray diffraction photograph of bone, it is concluded that the bone crystallites, i.e. the collagen-hydroxyapatite composite crystallites, are oriented with their unit cellc-axes spreading symmetrically around a distribution symmetry axis with a characteristic angular dispersion around this axis. An X-ray diffraction technique is then developed in order to measure accurately both the position of the distribution symmetry axis and the crystallites orientation distribution function. Typical results for samples from bovine femur are presented.

Some studies related to electricity generation from biological fuel cells and galvanic cells, in vitro and in vivo.

Abstract: A biological fuel cell such as an oxygen/glucose cell has been considered to be an ideal power source for implantable cardiac pacemakers and similar devices. This study is mainly concerned with the development of a single oxygen/glucose cell, which can be implanted inside the body fluids with the simultaneous presence of oxidant and fuel(s). Present results ofin vitro experiments with a single oxygen/glucose cell consisting of a platinum black on platinum-mesh electrode (cathode) and a platinum black on porous-graphite electrode (anode) have shown that cell performance was markedly increased after glucose addition. Half-cell testings by means of a potentiostat coupled to a linear sweep generator also demonstrated that the anode current of a platinised graphite electrode after glucose was over 3 mA/cm2. It was also found that a steady and continuous power output of 20 μW/cm2 could be generated from the above oxygen/glucose cell. When the cell was testedin vivo in the rat. the continuous power output was steady at 3·3 μW/cm2. The present study also investigated the possibility of generating electricity from an oxygen concentration cell and an oxygen/hydrogen cell. It was concluded that a platinum black on porous graphite electrode offers promise as a specific electrode for glucose oxidation. An oxygen/hydrogen cell could also provide a long termin vivo power supply provided the Pd-H electrode is properly encapsulated. The significance of the present study in relation to the development of biological power sources is discussed, and the importance of fundamental investigation for the development of a specific electrode is emphasised.

Hydromechanical simulation of systemic circulation.

Abstract: A hydromechanical model is developed for the simulation of the arterial systemic circulation. The geometry and elastic properties of arteries, the pulse-rate and stroke volume of the left ventricle, the design of peripheral resistances and the viscosity of the model fluid are approximated to physiological conditions.

Quantitative image analyser using a colour-television display for medical applications.

Abstract: The equipment has been developed to make quantitative measurements on slides, transparencies, agar cultures and similar biological preparations. The object is viewed by a monochromatic television camera, and the image is displayed on a colour-television monitor; the colours on this image are related to the light intensity at each part of the image and not to its actual colour. A 7-colour density-contour map is presented on the screen of the monitor. The following characteristics of regions of equal density are determined by electronic processing of the television image, and are digitally displayed and may be recorded on punched tape for subsequent computer analysis:

Analysis of the size and shape of cross-sections of muscle fibres.

Abstract: A method to record and describe the contours of cross-sections of muscle fibres from enlarged photographs has been developed. With the aid of a computer, different parameters describing the size and the shape of the fibres were calculated. The relevance and the accuracy of these parameters are discussed. Measurements of the cross-sections of fibres of quadriceps muscles in one normal and in two pathological cases have been taken. Histograms are presented to give an impression of the calculated parameters.

Phaseless recursive filtering applied to chestwall displacements and velocities, using accelerometers.

Abstract: This paper describes a digital technique to obtain chestwall velocities and displacements (1–200 Hz) due to the heart by integrating acceleration recordings. To suppress respiration and other slow movements, a phaseless filter technique based on a forward and backward procedure is described. This technique shows a clear improvement over the additive Archambaud method. The effect of the quantised input signal is computed and some practical and theoretical examples are given.

The stability of tantalum-pentoxide films in vivo.

Abstract: Sintered tantalum electrodes coated with tantalum pentoxide films can perform stably as anodes when implanted into biological tissues, and probably always do. Capacitances and leakages do not differ much from those obtained in conventional electrolytes. Such electrodes should be useful for implanted stimulators where space is short.

Strain-gauge versus water plethysmography. Description of simplified systems and analysis of differences and accuracy.

Abstract: Recently developed water and strain-gauge plethysmographs are compared on the same forearm. They do not differ systematically in absolute blood-flow values at different steady-state levels, provided that the strain gauge is applied at the middle, muscular, part of the forearm. The accuracy of the water and strain-gauge plethysmograph is identical, and the two instruments closely follow random variations in blood flow. The water plethysmograph is a reliable integrator of blood flow in a segment of a limb, and the strain-gauge described here can be used as an adequate substitute, when placed in the middle of the limb segment examined. However, the results from the strain-gauge plethysmograph are dependent on the actual location of the strain gauge.

Comparison of several pulse-pressure techniques for monitoring stroke volume.

Abstract: Values of stroke volume calculated from five different formulas utilising parameters derived from the aortic-pressure pulse waveform were compared with stroke-volume values calculated from the thoracic electrical-impedance waveform, which was recorded simultaneously with the aortic-pressure waveform. A total of 195 beats from three closed-chest anaesthetised dogs were compared. During the recording of the impedance and blood-pressure waveforms, the cardiac output was measured by dye and saline dilution. The mean of stroke-volume values from the impedance method was 39% greater than the mean ‘stroke volume’ calculated by dividing the dye cardiac-output value by the mean heartrate measured during the recording of the dye-dilution curve. The correlation between impedance and dye cardiac-output values was 0·879. The correlation of dye ‘stroke volume’ with values calculated by all four formulas was about 0·89. Individual stroke volumes could be markedly affected by variations in the beat-by-beat values of the total systemic resistance.

Static hysteresis loop of electrically stimulated muscles.

Abstract: The paper discusses the existence of a static hysteresis loop of a functionally electrically stimulated (f.e.s.) muscle. Hysteresis was observed in the relation between the amplitude of the stimulation pulses by which the muscles peroneus and tibialis anterior were stimulated, and the resulting dorsal flexion moment in the ankle joint. An attempt was made to prove the existence of a static hysteresis loop by two methods. With the first method, the disturbing influence of the time delay between the stimulation voltage and isometric moment was taken into account, and the fatigue during measurements was neglected. With the second method, both problems were avoided by fast sampling of the static hysteresis loop. It was found that the static hysteresis loop exists, that its average width amounts to 9% of the maximum isometric moment and that its form strongly depends on the experimental subject and on the position of the stimulation electrodes. The width of the loop and the deviations that result from the unrepeatability of the f.e.s. responses are of the same order. Therefore the static hysteresis loop, with the present state of the f.e.s. technology, is not important in the modelling of the f.e.s. muscles.

A mathematical model for the ultrasonic measurement of respiratory flow.

Abstract: A mathematical model is developed for the measurement of respiratory air flow, based on the phase shift of ultrasonic pulse trains. A correction is made for the velocity of found as a function of gas composition, moisture, temperature and pressure. Error estimates and calibration procedures as they relate to clinical application are discussed.

An application of aeronautical techniques to physiology. 1. The human microenvironment and convective heat transfer.

Abstract: The human body is surrounded by an enveiope of upward-moving warm air which forms a natural convection boundary layer. A Schlieren optical system has been used to visualise this airflow and this visualisation has been complemented by measurements of temperature and velocity within the flow and local convective heat transfer rates at the skin surface.

A new method for localised spinal-cord cooling.

Abstract: Hypothermia reduces ischaemic damage to nervous tissue and decreases cerebral oedema. Selective spinal-cord cooling has therefore been proposed as a means of treatment in spinalcord trauma. A miniature heat exchanger, made of Silastic, has been developed that can rapidly induce a central cord temperature of 17°C and may be left in place for several days without complication.

Computer-generated optokinetic display

Abstract: A digital computer was used to generate moving patterns which were projected onto a screen to serve as an optokinetic stimulus. Patterns, speed or direction of the stimulus can be changed almost instantaneously. On-line control of the computer-generated stimulus by the eye-position signal makes it possible to produce selective stimulation of particular regions of the retina.